Electron-beam exposure devices have been found to be a useful tool in providing controlled line exposures of submicron dimensions. Such dimensions, accompanied by strict tolerances, are essential to the production of integrated circuit chips. The procedure is to expose negative-working resists applied to suitable substrates, to electron beams having widths of submicron dimensions. After the resist is developed, the substrate not protected by the resist is etched, usually by a chemical or plasma etching. Examples of such procedures, including the exposure and development of the resist, are described in J. Vac. Sci. Technol., Vol. 15, No. 3, pp. 960-964 (May/June 1979).
One of the difficulties with such a procedure is the scarcity of useful negative-working resists. Not only must the resist demonstrate sensitivity to an electron beam of conventional voltage, but it must also resist deformation and dissolution by the etching process applied to the substrate or base material, usually a semiconductor. More specifically, it is preferred that, for direct writing application the resist have a sensitivity of at least about 2.0.times.10.sup.-7 coulombs/cm.sup.2 at 10 keV, a submicron resolution capability, thermal stability, and a resistance to etching. Such requirements are particularly difficult to achieve in light of the fact that prior studies have suggested that sensitivities in the 10.sup.-8 coulombs/cm.sup.2 range produce thermal instability.
A few acrylate copolymers have been described as useful electron-beam resists. Poly(glycidyl methacrylate-coethyl acrylate) is mentioned in the aforesaid article in J. Vac. Sci. Technol. However, its sensitivity achieves the desired value of 2.times.10.sup.-7 coulombs/cm.sup.2 at 10 keV, only at relatively high molecular weights. Furthermore, its resistance to plasma etching is not as good as is desired.
An additional poly(acrylate) described as sensitive to electron-beam exposure is a copolymer of 2-hydroxyethyl acrylate and saturated vinyls such as methyl methacrylate and butyl methacrylate. Examples are listed in British Patent Specification No. 1,407,312, but as paints rather than as resists. Of interest is the fact that this patent discredits the hydroxyethyl methacrylate homolog copolymer as being too insensitive to be useful.
Therefore, what is desired is a negative-working resist having a sensitivity to electron beams of at least 2.times.10.sup.-7 coulombs/cm.sup.2 at molecular weights less than 100,000, improved plasma etch resistance, and adequate submicron resolution capability.